My Cydia app "Signal 2" is out now, working on both GSM and CDMA devices now! Provides info about your cell connection and nearby towers.
About Signal 2:
Signal 2 displays information about the cell tower your iPhone is connected to as well as neighbouring cells. It detects and maps the location of all nearby cell towers so that the user can easily get a good idea of their cellular coverage or where to go to get the best cellphone reception. Combined with the free iPhone carrier unlock that planetbeing has helped create, a user can swap SIMs and determine which carrier is best for him or her based on cellular coverage. In addition the map, other useful technical data is displayed including RSCP (signal strength) in dBm and Ec/N0 (signal quality) to all neighbours, the PSC of the cells, as well as the frequency each cell is broadcasting in.
You can get Signal 2 ($3.99) from the Cydia Store for jailbroken iOS devices with cellular radios running iOS 5 and above.